262 ARTICULATIONS. 



1. SYNARTHROSIS. IMMOVABLE ARTICULATIONS. 



Synarthrosis includes all those articulations in which the surfaces of the bones 

 are in almost direct contact, not separated by an intervening synovial cavity, 

 and immovably connected with each other, as the joints between the bones of 

 the cranium and face, excepting those of the lower jaw. The varieties of synar- 

 throsis are three in number: Sutura, Schindylesis, and Gomphosis. 



Sutura (a seam). Where the articulating surfaces are connected by a series 

 of processes and indentations interlocked together, it is termed sutura vera; 

 of which there are three varieties: sutura dentata, serrata, and limbosa. The 

 surfaces of the bones are not in direct contact, being separated by a layer of 

 membrane continuous externally with the pericranium, internally with the dura 

 mater. The sutura dentata (dens, a tooth) is so called from the tooth-like form 

 of the projecting articular processes, as in the suture between the parietal 

 bones. In the sutura serrata (serra, a saw), the edges of the two bones forming 

 the articulation are serrated like the teeth of a fine saw, as between the two 

 portions of the frontal bone. In the sutura limbosa (limbus, a selvage), besides 

 the dentated processes, there is a certain degree of bevelling of the articular 

 surfaces, so that the bones overlap one another, as in the suture between the 

 parietal and frontal bones. When the. articulation is formed by roughened sur- 

 faces placed in apposition with one another, it is termed the false suture, sutura 

 notha, of which there are two kinds . the sutura squamosa (squama, a scale), 

 formed by the overlapping of two contiguous bones by broad bevelled margins, 

 as in the temporo-parietal (squamous) suture; and the sutura harmonia (dp^oi/ia, 

 a joining together), where there is simple apposition of two contiguous rough 

 bony surfaces, as in the articulation between the two superior maxillary bones, 

 or of the horizontal plates of the palate. 



Schindylesis (ax^v^a^, a fissure) is that form of articulation in which a thin 

 plate of bone is received into a cleft or fissure formed by the separation of two 

 laminae of another, as in the articulation of the rostrum of the sphenoid, and 

 perpendicular plate of the ethmoid with the vomer, or in the reception of the 

 latter in the fissure between the superior maxillary and palate bones. 



Gomphosis (yo^oj, a nail) is an articulation formed by the insertion of a conical 

 process into a socket, as a nail is driven into a board; this is not illustrated by 

 any articulations between bones, properly so called, but is seen in the articula- 

 tion of the teeth with the alveoli of the maxillary bones. 



2. AMPHIARTHROSIS. MIXED ARTICULATIONS. 



In this form of articulation, the contiguous osseous surfaces are connected 

 together by broad flattened disks of fibro-cartilage, which adhere to the ends 

 of both bones, as in the articulation between the bodies of the vertebra?, and 

 first two pieces of the sternum; or the articulating surfaces are covered with 

 fibro-cartilage, partially lined by synovial membrane, and connected together 

 by external ligaments, as in the sacro-iliac and pubic symphyses ; both these 

 forms being capable of limited motion in every direction. The former resemble 

 the synarthrodial joints in the continuity of their surfaces, and absence of 

 synovial sac; the latter, the diarthrodial. These joints occasionally become 

 obliterated in old age; as is frequently the case in the pubic articulation, and 

 occasionally in the intervertebral and sacro-iliac. 



3. DIARTHROSIS. MOVABLE ARTICULATIONS. 



This form of articulation includes the greater number of joints in the body, 

 mobility being their distinguishing character. They are formed by the approxi- 

 mation of two contiguous bony surfaces, covered with cartilage, connected by 

 ligaments, and lined by synovial membrane. The varieties of joints in this 



